Certain embodiments of the present invention generally relate to x-ray systems utilizing a solid state multiple element x-ray detector for producing an image; and more particularly, to techniques and apparatus for acquiring a series of images representative of a region of interest smaller than the x-ray detector.
Solid state x-ray detectors that comprise a two dimensional array of detector elements arranged in rows and columns are known in the art. A scintillator, such as Cesium Iodide (CsI), is deposited over the detector elements. The CsI absorbs x-rays and converts the x-rays to light, which is then detected by the detector elements.
Each detector element comprises a photodiode, which acts as a capacitor and stores charge representative of an amount of radiation incident on the detector element, and a field effect transistor (FET) that operates as a switch to enable and disable read out of the charge stored on the photodiode. Each detector element is connected to both a row, or scan line, and a column, or data line. The scan and data lines are used to activate the FET and read the level of stored charge in the photodiode.
Electronic noise caused by resistance and capacitance in the data lines may negatively impact the image quality of the detector. The amount of resistance and capacitance in the data lines decreases as the length of the data lines decreases. Therefore, in order to minimize the electronic noise and thus improve the image quality of the detector, the detector was designed with a split in each data line at the midpoint to reduce its length, effectively splitting the reading of the detector into two separate operations.
After an exposure, the detector is read on a row by row basis and digitized for further image processing, storage, and display. With a detector that has split data lines, two rows may be read at the same time. Two sets of read out electronics on two sides of the detector are required, rather than one set if the data lines are not split. Therefore, in order to achieve the same detector read out rate, or acquisition frame rate, the speed of the read out electronics may need to be only half what would be required of the read out electronics with unsplit data lines.
Several applications of the solid state detector are thoracic, vascular, and cardiac imaging. The entire detector field of view (FOV) may be utilized to acquire diagnostic data during thoracic applications. However, vascular and cardiac applications are interested in events that occur over time in regions of the body that may not require the entire detector FOV but do require a high frame rate.
Unfortunately, it is not always possible to have multiple x-ray detectors and systems dedicated to specific applications. When a specific application is targeted, detector design tradeoffs such as the area to be covered, pixel size, dynamic range, and acquisition frame rate are made to optimize the detector""s performance in regards to that application. For example, small pixel size, providing superior spatial resolution, comes at the cost of frame rate for a given size detector, or conversely, at the increased cost of wider bandwidth as well as increased cost of more channels (both read out and FET drive electronics). Large dynamic range, given that more conversion levels take more time, will also adversely impact frame rate. For a given pixel size, a larger detector will cost more for the required support electronics, and will not support frame rates as fast as a smaller detector that has the same Therefore, larger detectors with small pixels, while desirable for thoracic applications, may not have the bandwidth to support higher frame rates, such as those desirable for cardiac applications. With a lower frame rate, less temporal information may be acquired over the same time span compared to a smaller detector that can be completely read out more quickly.
Efforts have been made to address the use of larger, fine resolution detectors in applications that require a smaller region of interest (ROI) and for which an increased frame rate is desired. A smaller ROI may be defined centered about the split in the data lines without any throughput penalty. The scan lines outside the ROI may be read or scrubbed to restore the charge during an x-ray exposure. However, the data is of no interest and may be discarded or not collected. Then, after the x-ray exposure, the scan lines inside the ROI are read.
In some instances however, due to patient positioning, it may be desirable to define a small ROI along one edge or in a corner of the detector rather than in the center. But defining a smaller ROI asymmetric about the split in the data lines will require more time to read the detector, adversely affecting the acquisition frame rate. The split data line design thus becomes a limitation with regards to the acquisition frame rate as the highest rate can only be achieved when the ROI incorporates an equal number of scan lines on each side of the split in the data lines. If a larger number of scan lines is desired on one side of the split than the other, the read out electronics will require more cycles of operation for the first side, while the read out electronics for the second side will be idle during a portion of the acquisition. This effectively reduces the throughput for the entire detector by a factor of two during the read out of every scan line on the first side for which there is no complimentary scan line on the second side.
Thus, a need exists in the industry for a detector designed to acquire images that utilize the entire field of view of the detector, in addition to acquiring a series of images utilizing a small region of interest and a high acquisition frame rate, regardless of the placement of the region of interest on the detector, to address the problems noted above and previously experienced.
In accordance with at least one embodiment, an x-ray detector is provided to acquire an image. The x-ray detector comprises detector elements that store a charge representative of an x-ray level. The detector elements are arranged in rows and columns. Scan lines are arranged in rows or columns and connect to the detector elements. First and second sets of sensing circuits are utilized to read the charge from the detector elements. A first set of data lines connects to the first set of sensing circuits and a second set of data lines connects to the second set of sensing circuits. At least one of the data lines from the first set of data lines is interspersed with the second set of data lines.
In accordance with at least one embodiment, an x-ray system used to produce an image is provided. The x-ray system includes an x-ray source for generating x-rays and a detector comprising detector elements arranged in rows and columns. The detector elements store charge representative of an x-ray level. The x-ray system also includes first and second sets of sensing circuits reading charge from first and second sets of detector elements, respectively. First and second sets of scan lines are provided comprising groups including at least one consecutive scan line connecting to each detector element in one of the rows and columns. The first and second sets of scan lines connect to the first and second sets of detector elements. The groups in the first set of scan lines are adjacent to and alternate with the groups in the second set of scan lines.
In accordance with at least one embodiment, a method for acquiring x-ray data within a region of interest is provided. A region of interest in an x-ray detector is defined. The region of interest includes detector elements connecting to data and scan lines which are perpendicular to each other and each cross one dimension of the x-ray detector. The scan lines form groups comprising at least one consecutive scan line. The x-ray detector is exposed to a radiation source. After the x-ray detector is exposed, levels of charge stored by detector elements included in first and second groups of scan lines are read simultaneously with first and second sensing circuits, respectively. Levels of charge stored by detector elements included in third and fourth groups of scan lines are then read simultaneously with first and second sensing circuits, respectively. The first and second groups of scan lines are adjacent and are included in the region of interest, and the third group of scan lines are adjacent to the second group of scan lines.